1. Field of the Invention
This invention relates to a crack-preventive substrate and process for fabricating a solder mask, and more particularly to a crack-preventive substrate and process that can prevent the solder mask in the device site region from cracking.
2. Description of Related Art
The packaging process of semiconductor is the final step in manufacturing IC (integrated circuit) products. The objectives of the packaging process of semiconductor are to provide a medium of electrical connection between the die and PCB (printed circuit board) or between the die and other appropriate devices, as well as to protect the die from being damaged or contaminated. As far as the general BGA (Ball Grid Array) packaging process is concerned, the devices are assembled by first mounting the dies on a surface at individual device site on a substrate strip, then, performing electrical connection between the dies and the substrate. Afterwards, the devices are assembled by performing encapsulating process to encase the devices etc. by molding compound, subsequently, performing a solder-ball planting process on the another surface of the substrate strip to form solder balls of BGA package. Finally, a singulating process is performed to separate the encapsulated devices from the substrate strip, thus to complete the assembling process of a BGA package.
In the conventional package, a solder mask layer is formed on each surface of the substrate strip for the purpose of protecting the circuitry on the substrate from being damaged or contaminated during the solder-ball planting process and plating process. In additions, the forming of the solder mask layer is to effectively isolate each of the circuit region lest the unnecessary electrical connections be occurred in order that the substrate has relatively high reliability and yield to facilitate the subsequent packaging process.
In general, the footprint of a die-bonded device site is in rectangular shape, and the device site is connected to the substrate at the four-corner only. Moreover, a typical punching tool for a singulating process has a right-angle cutting edge corresponding to each corner of the device site. In the singulating process, the device will be excised from the substrate through the four-corner of the device site.
During a series of packaging process, the stresses resulted from each handling step and the thermal stresses will generate crack lines on the solder mask layer at the perimeter of the substrate. The crack lines started from the perimeter of the substrate will develop through the connection between the substrate and the device site toward the device site, thereby, will cause the exposure of the circuit region of the device site. Consequently, through the gap of the crack lines, the device will be damaged and contaminated by the exterior moisture, dust etc. that will cause the cracking of the solder mask layer in the subsequent high temperature process, thus the yield will be lowered.